1. Field of the Invention
The present invention relates to semiconductor laser devices, and more particularly to semiconductor laser devices used as pumping light sources, including solid lasers such as Nd- or Yb-doped YAG lasers, Yb-doped fiber lasers, and Er-doped fiber amplifiers.
2. Background Art
Semiconductor laser devices have been widely used as light sources for optical communications. For example, a conventional 940 nm semiconductor laser device has a structure made up of: an n-type GaAs substrate; an n-electrode disposed on one principal surface of the n-type GaAs substrate; and an n-type Al0.7Ga0.3As cladding layer, an Al0.35Ga0.65As guiding layer, a GaAsP barrier layer, an InGaAs active layer, another GaAsP barrier layer, another Al0.35Ga0.65As guiding layer, a p-type Al0.7Ga0.3As cladding layer, a p-type GaAs contact layer, and a p-electrode, sequentially disposed on the other principal surface of the n-type GaAs substrate. (See, e.g., A. Knigge et al., “100 W output power from passively cooled laser bar with 30% filling factor,” Conference Digest of 2004 IEEE 19th International Semiconductor Laser Conference, Kunibiki Messe, Matsue-shi, Simane Pref., Japan, ThA1, pp. 35-36, September 2004.)
However, this semiconductor laser device has reliability problems, since it includes Al (aluminum) near the active layer.
Further, in recent years there has been an increasing need for semiconductor lasers having a high electrical-to-optical power conversion efficiency, in order to reduce power consumption. However, we are already approaching the point where the slope efficiency of a semiconductor laser device can no longer be improved by increasing the internal quantum efficiency or reducing losses. Therefore, some other method must be found to further enhance the electrical-to-optical power conversion efficiency.